Advanced natural hydrated iron-alum oxides cation exchange resin for simultaneous phosphate and hardness removal

In this study, a hydrated iron-alum oxides-contained cation exchange resin (HIAO/225H) was synthesized for the first time from natural alum-ferric water of acid sulfate soil to improve the water quality. The HIAO/225H material was then characterized by FTIR, XRD, SEM, and EDX-mapping techniques and applied for phosphate and hardness removal tests. The phosphate removal by the HIAO/225H material reached equilibrium after 50 h with the highest adsorption capacity of 2.075 mg P g −1 (e.g., 69.16 mg P g −1 Fe) at pH 6, which was 1.12, 11.15, and 2.11 times higher than by hydrated ferric oxide/225H material, anion exchange resin (Akualite A420), and amphoteric ion exchange resin (MB6SR), respectively, under the same experimental conditions. The reason for the higher phosphate adsorption efficiency of HIAO/225H than the hydrated ferric oxide/225H material may be that HIAO contains Ca, Mg, and Al elements, leading to an easy formation of FeOOH on the surface. Particularly, HIAO/225H material was also effective for both hardness and phosphate removal with an adsorption capacity of 15.6 mg Ca g −1 , 9.4 mg Mg g −1 , and 1.825 mg P g −1 , which is higher 1.2 times than the phosphate removal only. This may be due to co-precipitation to form Ca 3 (PO 4 ) 2 and Mg 3 (PO 4 ) 2 with the support of cation exchange resins. These results showed that the HIAO/225H material has a good performance in removing both phosphate and hardness, which could be applied in practical water and advanced wastewater treatment.